Remorse: A deep, prolonged regret for wrong-doing whose damage cannot be repaired.Usage: Today's word has several near synonyms.

"Regret" is a plain sense of sorrow for offensive or immoral behavior.

"Penitence" is a sincere admission of transgression with an implication that the penitent intends to undertake moral improvement.

"Contrition" is an absolute relinquishment of self to complete and perfect penitence for misdeeds.

"Compunction" is a simple pang of conscience for a contemplated action of questionable morality. The adjective from today's word is "remorseful."

Suggested Usage: Ogden Nash thought remorse "a violent dyspepsia of the mind" but added, "One man’s remorse is another man’s reminiscence." However, there is too little evidence of it in contemporary society, perhaps the fact that led Tom Clancy to write the book, 'Without Remorse.' We have a growing list of real and fictional heroes who resort to violence without any remorse for the consequences. This leaves me a bit remorseful myself.
Source: Your Dictionary